I would think this would be a neat addition, or just a nice challenge, stupid idea? Maybe. But I'm probably sure some people would like this feature even if its 5% or less of current population. So here are some ideas that could go into it but thought of two different versions of it.
1.You die that's its no restart, no revives, dead
2.You die your character resets all the way back to 1 with all content reset as well
Either option will work though i think 2 may be harder to work with if it appears at all.
Challenges
-Can't form/join a party
-Map function removed
-Echo Buff does not apply(Primals/Coil)
-Lose in PvP you die
-Have to choose a job at beginning(MNK,BRD,WAR) and you will be gated by the classes that make it up Ex) WAR, has MRD(duh), GLD, and PUG you will only be able to use these classes during HC
-Can't trade with other players
-Rested Bonus does not apply
-2x the EXP to level up
Rewards
-Unique Titles(I know not one of the best things but something)
-Bards for your Choco Buddy
-Unique Achievements/Items for said Achievements
-Unique Mount
-Tome count doubled
Again these are just some ideas, have a better idea? Post away! Don't like what you see? Post away! A good portion of these ideas do come from two MMO's so giving credit to where credits due the two MMO's in question is Diablo(suprise) and a Korean MMOARPG Dungeon Fighter.
Again this is just something that would be nice to have thoughts?
Edit: Forgot to mention but due to the fact you can't form/join partys you will be gated from coil and will be at the complete mercy that is duty finder. This may be a double negative cause i mean says can't join party, does roulette means joining a party, yes and no what i mean by the whole not joining/forming is the Party finder feature and duty finder is a nice challenge cause you have no idea what your gonna end up with either a god send or a personal ticket to hell itself.